When to use this calculator
- Before setting a new health goal or checking whether a plan is realistic.
- When you want a quick baseline before discussing the result with a professional.
- When you are starting a fitness or diet programme and want a starting measurement.
- When you want to recheck the numbers after several weeks of change.
A worked example
These are the example figures the calculator opens with.
| Input | Value |
|---|---|
| Weight (kg) | 80 |
| Height (cm) | 178 |
| Neck Circumference (cm) | 38 |
| Waist Circumference (cm) | 88 |
For those figures the calculator returns:
- Body fat: 18.70%
- Fat mass: 14.96kg
- Lean mass: 65.04kg
Method & assumptions
This calculator estimates body fat percentage using circumference-based measurements, most commonly the US Navy method, which uses measurements of the neck, waist, and hips (for women) alongside height to derive an estimate. The underlying formula was developed and validated by the US Navy as a practical field assessment tool. While it avoids the need for specialist equipment, it is less precise than clinical methods such as DEXA scanning. Circumference measurements are sensitive to measurement technique — small errors in tape placement can shift the result by several percentage points. Treat your result as a useful guide for monitoring trends over time rather than as a clinically precise figure. For accurate body composition assessment, consult a healthcare professional.
Common mistakes
- Using an assumption that is not supported by a current local quote, bill, statement or official source.
- Treating a generic estimate as a lender, provider, payroll or tax authority decision.
- Mixing monthly and annual inputs without converting them consistently.
- Testing only one scenario instead of checking how a cautious assumption changes the result.
What to do next
- Run a second scenario with a cautious assumption so you can see the downside clearly.
- Compare the result with the related calculators below before making a decision.
- Check current local rules, eligibility and provider terms before applying or committing money.
- Keep a record of the assumptions so you can update the estimate when a quote, bill or pay figure changes.
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